Hydraulic steering powke



L. R. TWYMAN HYDRAULIC STEERING POWER TRANSMISSION Nov. 8, 1949 3 Sheets-Sheet 1 Filed Oct. 18, 1946 kw INVENTOR.

9 L.RAYMOND TWYMAN 3 Sheets-Sheet 2 INVENTOR.

FITTURNEH Nov. 8, 1949 1.. R. TWYMAN HYDRAULIC STEERING POWER TRANSMISSION Filed on. 18, 1946 mm i L RAYMOND TWYMAN WXT Nov. 8, 1949 L. R. TWYMAN HYDRAULIC STEERING POWER TRANSMISSION Filed Oct. 18, 1946 3 Sheets-Sheet 3 Patented Nov. 8; 1949 HYDRAULIC s'rnsnmo Pom rasnsmssron L. Raymond Twyman, Bloomfield Township, Oakland County, Mich, mignor to Victor: Incorporated, Detroit, Mich a corporation of Michltan Application mm- 18.1940, Serial No. 104.1111

11 Claims. (cl. 180-793) This invention relates to power transmissions, particularly to those Of the type comprising two or more fluid pressure energy translating devices, one of which may function as a pump and another as a fluid motor.

This invention particularly relates to a hydraulic power transmission system for power steering the dirigible wheels of a vehicle and for providing snubbing action for preventing too rapid directional change of said wheels.

It is well known that in manually steering a vehicle considerably more effort is required to steer the vehicle while at rest than while in motion because of the difference in the resistance against the steering efiort caused by static and dynamic friction. It is also well known that the dynamic frictional resistance opposed to the manual steering effort decreases as the speed of the vehicle increases.

In the past where means have been provided for power steering of a vehicle, it has been the custom to provide for power steering at all speeds of the vehicle. Where this was accomplished hydraulically, and a fixed displacement pump driven by the engine was used with a power booster associated with the dirigible wheels and the manual steering mechanism, the power steering of the dirigible Wheels was accelerated proportionately to the acceleration of engine speed because of the increased displacement of the pump. This problem of accelerated speed of power steering proportionate to increased engine speed was solved in some cases by the use of a variable delivery pump which materially increased the cost of power steering because of the difference in cost between fixed displacement and variable displacement pumps.

It is therefore an object of this invention ;to provide a hydraulic power transmission system for power steering the dirigible wheels of a vehicle when the vehicle is at rest and moving at low speeds.

It is also an object of this invention to provide a hydraulic power transmission system for the above purpose which will furnish safety snubbing action at high speeds for preventing too rapid directional change of the dirigible wheels in case of a tire blow out or the meeting of road obstructions by said wheels.

It is a further object of this invention to provide a hydraulic transmission incorporating a fluid pump and servo-motor for power steering of the dirigible wheels of a vehicle which will actuate the motor for power steering only at low vehicle speeds when the frictional resistance against 2 manual steering is the greatest and which will inactivate the motor for power steering at higher speeds when power steering is not necessary.

Further objects and advantages of the present invention will be apparent from the following description, reference being bad to the accompanying drawings wherein a preferred form of the present invention is clearly shown.

In the drawings:

Figure 1 is a diagrammatic view or the chassis or a vehicle incorporating a hydraulic power transmission system embodying a preferred form of the present invention.

Figure 2 is a view taken from line 2-2 of Figure 1.

Figure 3 is a sectional view of a servo-motor incorporated in the hydraulic transmission shown in Figure 1.

Figure 4 is an elevational view of the servo-motor shown in Figure 2.

Figure 5 is a sectional view taken on line 55 of Figure 3.

Figure 6 is a sectional view or a control valve incorporated in the hydraulic transmission shown in Figure 1.

Referring now to Figure 1, there is shown the chassis of a vehicle, the dirigible wheels In of which are connected by means of a drag link ii to one end 0! a servo-motor l4, the opposite end of which is connected to the chassis by means of a universal joint l6 connected to a piston rod l8 extending from the motor 14. The dirigible wheels l0 may be manually steered by means of a steering wheel 20 connected to a steering post '22 having a worm 24 which meshes with a steering sector 26, the latter of which is rigidly connected to a Pitman steering arm 28 by means of a squared shaft. The Pitman arm 28 is connected at its opposite end to the booster 14 by means of a ball 30. l

A fixed displacement pump 32 connected to a tank, not shown, by means of a conduit 34 is driven by the vehicle engine indicated by the numeral 36 in the well known manner. A pressure delivery conduit 38 connected to pump 32 is connected to a pressure port 40 of a pressure responsive control valve 42. The valve 42 in one position will direct pressure fluid to a pressure port 44 of the servo-motor l4 by means of a flexible conduit 46 connected to a motor port 4'! of the valve 42 and in another position will by-pass the steering shall only take place at low vehicle speeds and while the vehicle is at rest with the engine running, means have been provided for cutting off the servo-motor I4 for use as a power :booster at higher speeds. Although several means may be adapted to perform this result, the invention in its preferred form makes use of hydraulic governor means which at a predetermined speed of the drivingwheels will shift the control valve 42 to cut off the power from pump 32 to the motor I4.

Hydraulic governor means for shifting the control valve 42 to by-pass the pump 32 to the tank is provided by means of a pump 50 of smaller capacity than pump 32 which is mounted on a speedometer drive housing of the vehicle indicated by the numeral and shown more clearly in Figure 2. A shaft 53 of the pump extends into the housing 5| so as to be driven by the speedometer drive gears, not shown, in a suitable manner. The speedometer drive gears are associated in the conventional manner, not shown, with a drive shaft 52 of the vehicle. Thus, the pump 50 is not only associated with the speedometer drive but also with the drive shaft of the vehicle and the displacement from'the pump 50 will increase as the speed of the vehicle increases.

The pump 50 is connected to the tank by means of a conduit 54 and a pump delivery conduit 56 thereof is connected to the tank and to the control valve 42. An adjustable orifice 58 incorporated in the pump delivery conduit 56 is so originally adjusted that the full delivery from pump 50 will be discharged to the tank at low speeds of the vehicle. However, at a predetermined higher speed of the driving wheels, indicated by the numeral 60, which are associated with the drive shaft 52, the adjustable orifice 58 will create a resistance to increased pump flow suflicient to divert pressure fluid from pump 50 to shift the control valve 42 so as to by-pass the flow from pump 32 to the tank. Both the pump 32 and the pump 50 have integral relief valves, indicated by the numerals 62 and 63, which will relieve excessive pressure fluid from said pumps to the tank by means of conduits 64 and 65 whenever a predetermined pressure has arisen in the system as determined by the setting of the valves.

Although several types of power steering servomotors or boosters may be used in the hydraulic power transmission shown in Figure 1, it is'preferred that a servo-motor constructed in accordance with the patent to Vickers No. 2,022,698 be used therein. In addition to the pressure port 44, the motor I4 also has a tank port 66 which is connected to the tank by means of a flexible conduit 68. As shown in Figure 3, servo-motor I4 comprises a cylinder I0 having a valve chamber I2 in which is reciprocably mounted a valve 14 having longitudinal grooves I6 formed between extreme end lands 18 and 80. The valve 14 is connected by means of a valve stem 82 with an actuating slide 84 contained in the cylinder 10 which is associated with a threaded projection extending from the cylinder, the former of which forms part of the drag link and which is bolted to the cylinder. Formed in the chamber 12 is a central annular recess 86 connected to the inlet port 44 and annular recesses at the right and left, respectively, thereof indicated by the numerals 88 and 90. In addition, annular recesses 9| and 93 are formed at the left and right end of valve 14 within the main chamber 12. The recess 88 communicates with a conduit 92 that in turn connects with a chamber 94 to the right of a piston 96 which is connected to the piston rod I8. The recess 90 connects by means of a conduit 98 with a chamber I00 to the left of the piston 96.

The ball 30 is connected by suitable bearing blocks and a pick-up spring I02 with the slide 84 which in turn connects with the valve stem 82. A centering spring I04 and discs I06 and I08 are positioned between the slide 84 and the valve I4.

In the neutral position with pump 32 connected to the port 44 of motor I4, valve "I4 is adapted to admit pressure fluid to chambers 94 and I00 to maintain the motor in a state of equilibrium resulting in directional stability of the dirigible wheels. When manually steering the vehicle in case of power failure at low speeds or when the displacement from pump 32 is bypassed around motor I4 at higher speeds, fluid may be displaced from and directed to the opposite chambers 94 and I00 by means of a check valve H0 and conduits shown more clearly in Figures 4 and 5.

A passageway II2 connects the annular chambers 9I and 93 and with the port 66 of motor I4 as best shown in dotted lines in Figure 4. The

check valve H0 is connected to the passage II2 to permit free flow to the port 44 by means of a passage II3 when pump pressure does not hold the check valve III! closed. The lands l8 and of valve I4 are very accurately related to the annular grooves 88 and 90, the latter being only slightly wider than the lands so as to leave a very small clearance on each side. In the neutral position of the valve I4, the ports created by this slight clearance are in effect orifices which cause a pressure to be built up on both sides of the piston 96 to keep the motor I4 in a state of equilibrium.

Referring now to Figures 1 and 6, control valve 42 comprises a housing II4 containing a valve spool II6 reciprocably mounted in a bore H8. The bore H8 is provided with an annular pressure port I20 connected to the pressure port 40, an annular motor port I22 connected to external motor port 41 and an annular tank port I24 connected to an external tank port I26. The spool H6 is provided with extreme right and left end lands I28 and I30, respectively, and is biased to the leftward position by means of a spring I32 of predetermined resistance mounted in the right end of bore II8, the latter of which is closed by a plug I34 adapted to limit rightward movement of spool II6.

Normally, pressure port 40 is connected to motor port 41 but by means of pressure fluid admitted to the left end of bore II8 by means of a port I36, the spool H6 may be shifted rightwardly to connect the pressure port 40 to tank port I26 while blocking the motor port 41. Fluid displaced from the right end of bore 8 is directed to the tank by means of a passage I38 connected to tank port I26.

Pressure fluid from the auxiliary pump 50 will shift the control valve 42 at a vehicular speed, or speed of the driving wheels of the vehicle, sufiicient to cause a displacement of the pump 50 which the orifice 5B is originally adjusted to resist.

In operation with the engine running and driving pump 32 and the vehicle at rest, the dirigible wheels I0 may be power steered as follows: Any turning of the steering wheel 20 will result in a movement of the valve 14 because of the drag link I2 being connected thereto by means of valve stem 82 and slide 84. If the valve I4 is moved, for instance to the left, pressure fluid from pump 32 is directed to chamber I33 and the left side of piston 33 to shift the cylinder 13 to the left. Pressure fluid from pump 32 is directed to chamber I33 by means of pump delivery conduit 33, control valve 42 (which is in the position shown in Figure 6), conduit 43, pressure port 44 of motor I4, recess 33, groove 13 of valve 14, recess 93 and conduit 93.

Displaced fluid from chamber 34 may flow to the tank by means of passage 32, recesses 33 and 33, passage II2, tank port 33 and conduit 33. If the valve I4 is moved to the right, pressure fluid from pump 32 is directed to the chamber 34 to the right of the piston 33 to shift the cylinder I3 to the right by means. of pressure port 44, central recess 36, grooves I3, recess 33 and conduit 32. Displaced fluid from chamber I33 may flow to the tank by means of conduit 33, recess 93, chamber 3|, passage II2, tank port 33 and conduit 68.

Immediately upon the valve being shifted slightly to the right to open up port 38 to chamber 34 or shifted to the left to open up port 93 to chamber I33, pressure fluid from pump 32 is admitted to the proper chamber in order to shift the cylinder 13 for power steering of the dirigible wheels I3. When the steering of wheel 23 ceases, there is a slight continued movement of the cylinder I3 to place the valve I4 again in a neutral position during which pressure fluid is admitted to both chambers I33 and 94 to hold the dirigible wheels in steered position. Any tendency of the cylinder 13 to drag the valve I4 along after the steering effort has ceased will be resisted by the light spring I34.

When the vehicle is in motion up to a predetermined speed of the driving wheels 83, the same action will take place, namely, immediate power steering of the dirigible wheels as previously described upon turning of the steering wheel 23 in either direction. In addition, in case of the meeting of road obstructions by the dirigible wheels or a sudden flat tire, a directional change of the dirigible wheels is resisted by equalized pressure in chambers 34 and I33. Any sudden shock tending to shift the cylinder 13 will open one of the small port openings of the valve 14 to cause a differential pressure to be immediately created tending to draw the drag link I2 and cylinder I3 back to neutral position to correct the direction of the wheels so as to give directional stability.

It should be noted that there is a sharp distinction between the relative movements of the cylinder I3 and the valve I4 when power steering the vehicle and in case of the dirigible wheels meeting sudden shocks. In the former case, upon aslight manual steering effort, the valve I4 will shift a slight fraction of an inch to open fully one of the ports 83 or 93 to pump 32 and the other port thereof to the tank and the cylinder I3 will immediately follow up the movement of the valve I4. Upon completion of the steering operation desired, there is a continued slight movement of the cylinder 13 so as to place the valve .14 again in the neutral position to hold the.

dirigible wheels on the steered course.

With the pump 32 connected to the port 44 of motor I4 when the dirigible wheels meet with sudden road shocks, however, the cylinder I3 rather than the valve I4 tends to move slightly which opens up one of the valve ports 33 or 93 to immediately cause a differential pressure to be created on opposite sides of the piston 33 and force the cylinder back in the opposite direction to again place the valve 14 in a neutral position.

Up to a predetermined speed of the driving wheels 33, the full displacement from the pump 53 is directed to the tank through the orifice 33. However, as the speed of the drive shaft increases the speed of the driving wheels will increase in proper ratio thereto and the displacement from the pump 53 will increase. When the speed of the driving wheels associated with the drive shaft reaches a predetermined maximum. the displace ment from pump 53 will be of such volume that the orifice 53 no longer will pass the complete displacement without creating a resistance sumcient to divert a portion of the flow from pump 53 to the pressure port 43 of valve 42. The resistance created by the orifice 53 results in a build-up of pressure suflicient to overcome the resistance of spring I32 to shift the valve spool II6 to the right. In this position of the spool II6, the land I33 blocks the pressure port 43 from communication with the motor port 41 and connects the pressure port 43 to the tank port I26 so as to by-pass the complete flow from the pump 32 to the tank and unload the pump.

It should now be noted that with the pump 32 cut off from the motor I4, that power steering of the dirigible wheels I3 is not possible. At and over a predetermined speed of the driving wheels 63, the displacement from pump 53 is greater than the orifice 58 is originally adjusted to pass without resulting in a continuous pressure at port I36 to keep spool II6 shifted to the right and causing the complete flow of fluid from pump 32 to be by-passed around the motor I4 to the tank.

Manual steering is not affected due to the manual steering mechanism being associated with the cylinder 13 which forms a part of the drag link I2 to the dirigible wheels. As in the former case of power steering when the steering wheel 23 is turned, the first movement will be that of the valve I4 followed almost immediately by movement together of the valve 14 and cylinder "I3. In manually steering the dirigible wheels, fluid may be displaced from one side to the other of the piston 96 by means of the by-pass check valve H3 and thepassages shown in Figures 4 and 5. when the cylinder moves leftwardly, fluid is displaced from chamber 34 to chamber I33 by means of conduit 92, annular recess 83, chamber 93, passage II2, check valve II3, passage II3, recess 86, groove 16 of valve 14, annular recess 33 and passage 38. When the cylinder moves rightwardly. fluid may be displaced from chamber I33 to chamber 94 by means of conduit 98, annular recess 33, chamber 9|, passage II2, check valve H3, passage II3, annular recess 86, groove I3, recess 88 and conduit 92.

Although pump 32 has been cut-off from motor I4 directional stability of the dirigible wheels will be maintained in a slightly different manner than described with the pump 32 connected to the motor I4 at low vehicle speeds.

Any tendency of the cylinder I3 to shift rightwardly or leftwardly when sudden road shocks are met by the dirigible wheels is almost impossilge/ftn fl uid to escape from chamber 84 pa that the dirigible wheels will be held on a steady course. If the dirigible wheels tend to shift the cylinder to the right, fluid must be displaced from chamber I00. After a slight fraction of an inch movement to the right of the cylinder 10, port 90 is fully open to recess 86 and port 44. As in the former instance due to the fact that port 41 of valve 42 is blocked by land I28 of spool H6 and check valve H prevents flow from passage H3 to passage H2, it is impossible for fluid to escape from chamber I00 so that similarly the wheels are again held on a steady course.

Consequently, although the motor 14 at higher speeds will not act as a booster for power steering of the dirigible wheels, it will act to prevent sudden directional change of the dirigible wheels caused by the meeting of road obstructions or tire blow-outs.

While the form of embodiment of the invention as herein disclosed constitutes a preferred form, it is to be understood that other forms might be adopted, all coming within the scope of the claims which follow.

What is claimed is as follows:

1. In a vehicle having mechanism for manual steering of the dirigible wheels thereof, a hydraulic power transmission system comprising in combination a fluid pump, hydraulic steering servo-motor means, control means connecting the pump to the motor for power steering the dirigible wheels, and means responsive at a predetermined speed of the vehicle for causing the control means to disconnect the pump from the motor and inactivate the motor for power steermg.

2. In a vehicle having mechanism for manual steering of the dirigible wheels thereof, a hydraulic power transmission system comprising in combination a fluid pump, hydraulic steering servo-motor means connected to the manual steering mechanism and the dirigible wheels and hydraulically connected to the pump to receive fluid therefrom, control means for activating the motor at low speeds of the vehicle for power steering of the dirigible wheels, and hydraulic governor means connected to the control means for inactivating the motor at a predetermined higher speed of the vehicle.

3. In a vehicle having mechanism for manual steering of the dirigible wheels thereof, a hydraulic power transmission system comprising in combination a fluid pump, hydraulic servomotor means connected to the manual steering mechanism and the dirigible wheels, a pressure responsive control valve biased to connect the pump to the motor for power steering the dirigible wheels and hydraulic governor means connected to the control valve for causing the latter at a predetermined speed of the vehicle to short circuit and inactivate the motor for power steering the dirigible wheels.

4. In a vehicle having mechanism for manual steering of the dirigible wheels thereof, a fluid pump, hydraulic steering servo-motor means connected to the manual steering mechanism and the dirigible wheels, the combination therewith of control valve means adapted to connect the pump to the motor for power steering of the vehicle and means responsive at a predetermined vehicular speed for shifting the control valve to short circuit the pump and inactivate the motor for power steering of the vehicle.

5. In a vehicle having an engine mechanically associated with the driving wheels of the vehicle and mechanism for manual steering mechanically associated with the dirigible wheels of the vehicle, a hydraulic power transmission system comprising in combination a fluid pump driven by the engine, hydraulic steering servomotor means connected to the steering mecha-- nism and the dirigible wheels, governor means connected to the driving wheels and means connected to the pump, motor and governor means for causing power steering of the dirigible wheels by the motor when the driving wheels are idle and rotating at low speeds and for inactivating the motor for power steering with the driving wheels rotating at apredetermined higher speed.

6. In a vehicle having an engine mechanically associated with the driving wheels of the vehicle and mechanism for manual steering connected to the dirigible wheels of the vehicle, a hydraulic power transmission system comprising in combination a fluid pump driven by the engine, hydraulic steering servo-motor means mechanically connected to the steering mechanism and the dirigible wheels, pressure responsive control valve means normally connecting the pump to the motor for power steering of the dirigible wheels and hydraulic governor means mechanically connected to the driving wheels and hydraulically connected to the control valve means and responsive at a predetermined speed of the driving wheels for shifting the control valve to short circuit the pump and inactivate the motor for power steering of the dirigible wheels.

7. In a vehicle having an engine and a drive shaft mechanically associated therewith and with the driving wheels of the vehicle a hydraulic power transmission system comprising in combination a fluid pump driven by the engine, hydraulic steering servo-motor means, control means for con-, necting the pump to the motor for power steering of the vehicle and governor means connected to the drive shaft and the control means for causing the control means to disconnect the pump from the motor at a predetermined speed of the vehicle.

mechanically associated therewith and with the driving wheels of the vehicle and mechanism for manual steering mechanically associated with the dirigible wheels of the vehicle, a hydraulic power transmission system comprising in combination a fluid pump driven by the engine, hydraulic steering servo-motor means mechanically connected to the steering mechanism and the dirigible wheels, control means connecting the pump to the motor for power steering of the dirigible wheels and governor means connected to the drive shaft and the control means for causing the control means to short circuit the pump and inactivate the motor for power steering at a predetermined vehicular speed.

9. In a vehicle having mechanism for manual steering of the dirigible wheels thereof, a fluid pump, and hydraulic servo-motor means connected to the manual steering mechanism and the dirigible wheels, said motor means including means for preventing rapid directional change of the dirigible wheels in case of motor inactivation, in combination therewith means for activating the motor at low vehicular speeds for power steering of the dirigible wheels and governor means connected to the activating means for inactivating the motor for power steering at a predetermined higher vehicular speed.

10. In a vehicle having an engine mechanically 8. In a vehicle having an engine, a drive shaft associated with the driving wheels of the vehicle and mechanism for manual steering mechanically associated with the dirigible wheels of the vehicle, a hydraulic power transmission system comprising in combination a fluid pump driven by the engine, hydraulic steering servo-motor means connected to the manual steering mechanism and the dirigible wheels adapted for power steering of the latter, said motor means including snubbing means for preventing too rapid directional change of the dirigible wheels when the motor is power inactivated, control means connected to the pump and motor for activating the motor for power steering when the engine is running and at low speeds of the driving wheels and governor means connected to the driving wheels and the control means for causing the control means to inactivate the motor for power steering at a predetermined higher speed of the driving wheels.

11. In a vehicle having mechanism for manual steering of the dirigible wheels thereof, a hydraulic power transmission system comprising in combination hydraulic steering servo-motor means connected to the manual steering mechanism and to the dirigible wheels, at fluid pump connected to the motor for activating the motor for power steering of the dirigible wheels, and hydraulic governor means responsive at a predetermined speed of the vehicle and disconnecting the pump from the motor for inactivating the motor.

L. RAYMOND TWYMAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,341,502 Ingres Feb. 8, 1944 2,356,492 Smith Aug. 22, 1944 

